I don't know what you mean by "they can burn fat at higher levels of intensity" but there comes a certain point of intensity where no one can use fat as the fuel, and have to rely on carbs/glucose.

If you don't know what I mean then I don't know what to tell you. That is about the simplest terms I can put it in for you. I would suggest you follow the link and look through the website to learn a bit more about how the metabolic process works in an athletic setting.

Edit: That actually sounds a bit snarky, and not how I meant it. Just see Owly bellow for further explanation.

If you don't know what I mean then I don't know what to tell you. That is about the simplest terms I can put it in for you. I would suggest you follow the link and look through the website to learn a bit more about how the metabolic process works in an athletic setting.

I think it was that your sentence was confusing and could be read as meaning the athlete would burn fat at the highest intensities (the aerobic cap), which of course does not make sense, nor does it reflect the content of your link. From what I understand from reading the post you linked, the author found that being ketoadapted allowed him to burn fat at higher levels of intensity than he would have been able to burn fat prior to ketoadaptation. This absolutely makes sense and is part of the theory of "train low, race high" that is used by some marathoners. The author still agrees that glycogen is needed at the very highest levels of exertion, which I think was where some readers of your statement got confused--I'm assuming this is what you were referring to as the times when glycogen is really needed.

That would still support the idea that someone doing HIIT or other very intense activity is going to need those glycogen stores for peak performance, while it would appear that endurance athletes can train their bodies to run primarily on fat as fuel for their races and that ketoadaptation may help with this process and may improve athletic performance in the endurance context (although most of the top athletes who use "train low, race high" are carb loading before race day because the extra fuelling helps provide better speed when it counts).

“If I didn't define myself for myself, I would be crunched into other people's fantasies for me and eaten alive.” --Audre Lorde

I think it was that your sentence was confusing and could be read as meaning the athlete would burn fat at the highest intensities (the aerobic cap).....
....The author still agrees that glycogen is needed at the very highest levels of exertion, which I think was where some readers of your statement got confused--I'm assuming this is what you were referring to as the times when glycogen is really needed.

Sorry if I was not clear. As you say train low and race high....and, "the author found that being ketoadapted allowed him to burn fat at higher levels of intensity than he would have been able to burn fat prior to ketoadaptation". That was actually my main point. Of course you reach a threshold where you become dependent on glucose, so you assume correct. I just redirect all questions to your answer to explain what I meant . Of course I was relying heavily on people following the link and putting more of that together on their own rather than spelling it out so well myself.